In the completion of oil and gas wells, it is customary to install a production packer between the production tubing and the well casing for the purpose of sealing off the high pressures of the producing formation to prevent those high fluid pressures from acting against the casing connections at the well head, and to prevent the application of such high fluid pressures to the long string of casing in place in the well bore, thereby reducing the likelihood of leaks occurring through such casing. It may become necessary from time to time to plug the production packer and temporarily suspend production to permit a service operation to be carried out, such as stimulation, or to permit venting of the casing pressure to the atmosphere so that the well head or a portion of the well tubing may be removed, or so that pressure applied above the plug may be used to test the casing, set the packer, or test the packer. Occasionally, it may be desirable to shut-in the well because of depletion or inadequate production from the formation, or because too much water is being produced from the formation.
It may be desirable to seal the well below the production packer, for example, when production is to be initiated from a higher formation interval. It is common practice to isolate the higher formation interval being completed with respect to the lower formation interval while completion is being carried out. Generally, this isolation is obtained by setting a production packer between the two intervals and temporarily plugging the packer mandrel bore with a packer plug. The packer plug is run into the well on a running tool and inserted into an upwardly facing landing receptacle or receiving head, thereby blocking flow communication through the packer mandrel. After the plug is latched into sealing engagement with the packer, the running tool is released and retrieved to the surface, leaving the plug so that it will seal the packer bore from pressure differentials, either above or below. Then the casing above the sealed packer is perforated by perforating guns, so that formation fluid can be produced from the upper formation interval.
Once the service operation is finished at the upper level, the packer plug is retrieved and the lower end of a string of production tubing is then coupled into the landing receptacle to reestablish flow communication from the lower formation interval to the surface. In a completion involving two production zones a dual bore packer is set in the well bore above the upper production interval, and formation fluid is produced from the two formation intervals through dual production tubing strings. If the lower formation interval is unproductive, the sealing plug is retained in the lower packer, and only the upper formation interval is produced.